1. Field of the Invention
This invention relates to a method of forming an interconnection of predetermined pattern on a substrate for interconnection metalization (hereinafter, termed "metalization substrate"). More particularly, it relates to a method of forming an interconnection of a predetermined pattern on a metalization substrate by a lift-off technology.
2. Brief Description of the Prior Art
First, a prior-art method of forming an interconnection based on the lift-off technology will be explained.
FIG. 1a illustrates a state in which a layer for lift-off 2 made of e.g. a polyimide resin is formed on a substrate 1 and a mask layer 3 made of chromium, aluminum or the like is formed thereon. The pattern of the mask layer is in a shape inverse to an interconnection pattern. Subsequently, as shown in FIG. 1b, the lift-off layer 2 is etched and processed into a shape conforming with the mask layer 3 by the use of an etching process such as e.g. RF sputter etching. Thereafter, metal layers for interconnection metalization 4a and 4b made of aluminum, copper, silicon or an alloy thereof are deposited. Further, as shown in FIG. 1c, the lift-off layer 2 underlying the mask is etched by using oxygen plasma 5 or the like. Simultaneously, the mask layer 3 and the overlying metal layer 4b are stripped off and removed. Then, a state shown in FIG. 1d is established, and an interconnection of the predetermined pattern is formed.
In such prior art, however, as shown in FIG. 1c, the area of the etched surface of the lift-off layer 2 is small, and the lateral distance to be etched is large. Therefore, a long time is required for removing the lift-off layer 2 with the oxygen plasma 5. By way of example, in the case of etching the lift-off layer 2 with the oxygen plasma, the rate at which the etching proceeds in the lateral direction is approximately 50 .mu.m/hr under conditions of an oxygen pressure of 5 to 10 Torr and a radio-frequency power of 300 to 500 watts. If the width S of the lift-off layer 2 shown in FIG. 1b is 300 .mu.m, it takes three hours to remove the lift-off layer. The exposure of the metal layer 4a to the oxygen plasma for the long period of three hours is unfavorable, not only in a low production efficiency, but also in the oxidation of the surface of the metal layer 4a, the production of a carbide or the occurrence of contamination attributed to the adhesion of a nonvolatile substance.
The following references are cited to show the state of the art; Japanese Patent Laying-open Specification No. 50-86984 and Japanese Patent Laying-open Specification No. 50-104870.